Harvesting, Transporting and Milling Methods Affect Oil Quality. It’s a FACT.

By Antoinette Addison
May 01, 2011

In previous issues of Pressing Times, we have discussed the impact that olive varietals and time of picking have on the quality and taste of olive oil. A third critical factor is the way the olives are processed into oil. Even the best fruit, picked at the optimum time, will not yield a good and healthy product without a good milling process. While many things that can be done during milling to increase the oil yield and decrease costs might increase profit, these practices also result in lowering the quality and the organoleptic characteristics of any extra virgin olive oil.

What are some important factors governing the quality of extra virgin olive oil?Let’s take a quick review from the time of picking to bottling.


  • Harvest is best done in a way that does not damage the fruit. Many techniques used for convenience or cost savings, such as letting the fruit fall to the ground on a tarp, result in bruising the fruit, which will cause increased acidity and lower the quality of oil.

  • Olives should be transported in low, well-ventilated containers and milled right away. Prolonged storage, or slow working of the fruit, lowers the quality of the oil. Oxidation and fermentation occur in the stored fruit, especially in high, non-ventilated harvest bins, which can lead to defects and off-flavors in oil. Even though it may be more convenient and cheaper to have the fruit stored for a while, growers serious about the quality of their product get their olives to the mill quickly and make sure that they are milled promptly.

  • Heating the olive paste during the milling process results in higher yields, so this technique is often used to increase profits. Quality extra virgin olive oil, however, comes from fruit that is processed at temperatures below 86°F. This is important for the protection of the aromas, flavors, and health benefits.

  • Another milling practice, adding water to the olive paste during the milling process, may increase yield, but like heating, it too results in lower oil quality and organoleptic characteristics.

  • During this whole process, keeping everything clean is critical since olive oil can so easily become contaminated by odors from the fermentation of waste products or any other factors. One of my favorite stories is having tasted oil that had been left in an open barrel next to a fire. It truly tasted and smelled of smoke.

  • Finally, storing the finished product with care is extremely important. It is fundamental to store extra virgin olive oil in clean stainless steel or in dark glass to protect the oil from the light. It is best stored at temperatures below 65°F. Most consumers, however, are more likely to buy a product that they can see, in clear glass, and this results in a tough decision for the producer: do what is best for the oil or what is most likely to sell the product? We believe that educating your customers about quality and explaining its characteristics is ultimately the best business practice.


As you can see, many ways to save money or increase yield result in a lower quality product. Making a true quality olive oil that your customers will appreciate means refusing to cut corners in the processing stage. This is why quality extra virgin olive oil costs more than mass-produced or lower quality olive oil. It is not cheap to make a great product.

For more about the factors governing the quality of extra virgin olive oil, read Making Perfect Olive Oil.